Portability: please allow to move VMs with Bridged NIC attached

Description

The key point of v4.0 architecture is portability. However the situation with bridged NICs disallows to port to a different host.

From original author, "NeBlackCat":

"When moving VMs back and forth between Windows and Linux hosts, or using a dual boot configuration, you're faced with the issue that NIC names will be different. In Windows, VirtualBox uses the immutable Windows-assigned NIC names (eg. "Atheros AR8121/AR8113/AR8114 PCI-E Ethernet Controller(NDIS6.20)") in its .vbox files, not the user rename-able friendly names (eg. "LAN", or even "eth0"), so you can't make them the same."